package com.aquarius.wizard.leetcode.tree;

import java.util.HashMap;
import java.util.Map;

public class TreeExamTwo {
    /**
   根据—棵树的中序遍历与后序遍历构造二叉树。你可以假设树中没有重复的元素。
   中序遍历inorder =[9,3,15,20,7]
   后序遍历postorder=[9,15,7,20,3]
    3
 9     20
     15   7
   */
    public TreeNode buildTree(int[] preorder, int preLeft, int preRight, Map<Integer, Integer> map, int inLeft, int inRight) {
        if (preLeft > preRight || inLeft > inRight) {
            return null;
        }
        int rootVal = preorder[preLeft];
        TreeNode root = new TreeNode(rootVal);
        int pIndex = map.get(rootVal);
        root.left = buildTree(preorder, preLeft + 1, pIndex - inLeft + preLeft, map, inLeft, pIndex - 1);
        root.right = buildTree(preorder, pIndex - inLeft + preLeft + 1, preRight, map, pIndex + 1, inRight);
        return root;
    }

    public TreeNode buildTree(int[] preorder, int[] inorder) {
        int preLen = preorder.length;
        int inLen = inorder.length;
        if (preLen != inLen) {
            throw new RuntimeException("两数组长度不等！");
        }
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < inLen; i++) {
            map.put(inorder[i], i);
        }
        return buildTree(preorder, 0, preLen - 1, map, 0, inLen - 1);
    }

    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode() { }
        TreeNode(int val) {
            this.val = val;
        }
        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
}
